Methods for three-dimensional (3-D) mapping of the endocardium (i.e., the inner surfaces of the heart) are known in the art. For example, U.S. Pat. No. 5,738,096, whose disclosure is incorporated herein by reference, describes a method for constructing a map of the heart. An invasive probe is brought into contact with multiple locations on the wall of the heart. The position of the invasive probe is determined for each location, and the positions are combined to form a structural map of at least a portion of the heart.
In some systems, such as the one described by U.S. Pat. No. 5,738,096 cited above, additional physiological properties, as well as local electrical activity on the surface of the heart, are also acquired by the catheter. A corresponding map incorporates the acquired local information.
Some systems use hybrid catheters that incorporate ultrasound imaging and position sensing, as well as electrical sensing. For example, U.S. Pat. No. 6,690,963, whose disclosure is incorporated herein by reference, describes a locating system for determining the location and orientation of an invasive medical instrument that may include an ultrasound imaging head, as well as an electrode.
A catheter with acoustic transducers may be used for non-contact imaging of the endocardium. For example, U.S. Pat. Nos. 6,716,166 and 6,773,402, whose disclosures are also incorporated herein by reference, describe a system for 3-D mapping and geometrical reconstruction of body cavities, particularly of the heart.
As another example, U.S. Pat. No. 5,876,345, whose disclosure is incorporated herein by reference, describes an ultrasonic catheter for two-dimensional (2-D) imaging or 3-D reconstruction. The ultrasonic catheter includes at least two ultrasonic arrays having good near and far field resolutions. The catheter provides an outline of a heart chamber, in order to assist in interpreting images obtained by the catheter.
Several methods are known in the art for non-contact reconstruction of the endocardial surface using intracardial ultrasonic imaging. For example, PCT Patent Publication WO 00/19908, whose disclosure is incorporated herein by reference, describes a steerable transducer array for intracardial ultrasonic imaging. The array forms an ultrasonic beam, which is steered in a desired direction by an active aperture. U.S. Pat. No. 6,004,269, whose disclosure is also incorporated herein by reference, describes an acoustic imaging system based on an ultrasound device that is incorporated into a catheter. The ultrasound device directs ultrasonic signals toward an internal structure in the heart to create an ultrasonic image.
PCT Patent Publication WO 99/55233, whose disclosure is incorporated herein by reference, describes a method for delineating a 3-D surface of a patient's heart. A 3-D mesh model is developed using training data, to serve as an archetypal shape for a population of patient hearts. Multiple ultrasound images of the patient's heart are taken in different image planes. Anatomical locations are manually identified in each of the images. The mesh model is rigidly aligned with the images, in respect to the predefined anatomical locations.
Other methods of contour extraction and 3-D modeling using ultrasonic images are described in European Patent Application EP 0961135, whose disclosure is incorporated herein by reference. As another example, PCT Patent Publication WO 98/46139, whose disclosure is also incorporated herein by reference, describes a method for combining Doppler and B-mode ultrasonic image signals into a single image using a modulated nonlinear mapping function.
U.S. Patent Application Publication 2006/0241445, whose disclosure is incorporated herein by reference, describes a method for modeling of an anatomical structure. A plurality of ultrasonic images of the anatomical structure are acquired using an ultrasonic sensor, at a respective plurality of spatial positions of the ultrasonic sensor. Location and orientation coordinates of the ultrasonic sensor are measured at each of the plurality of spatial positions. Contours-of-interest that refer to features of the anatomical structure are marked in one or more of the ultrasonic images. A three-dimensional (3-D) model of the anatomical structure is constructed, based on the contours-of-interest and on the measured location and orientation coordinates.
Other patents and patent applications of relevance to the present invention include U.S. Pat. No. 6,139,500, U.S. Patent Application Publication 2005/0283075, U.S. Pat. Nos. 6,447,453 and 6,447,454, U.S. Patent Application Publication 2005/014377, U.S. Patent Application Publication 2005/0137661, and U.S. Pat. No. 6,556,695, all of which are incorporated herein by reference.